1. Field of the invention
The present invention relates to a cover for adjusting the bend of an image original in an image reader which reads the reflected light obtained by lightening from underneath a transparency board on which an image original is placed.
2. Description of the Prior Art
The detail of a prior image reader 2 is shown in FIG. 1. A transparency board 6 is located on the top of a body 4. An image is described onto an opaque base sheet such as printing paper, mechanical. The opaque paper is referred to as a "reflection original" hereinafter. The reflection original to be read is placed face down on the transparency board 6. Then, the reflection original is covered with a cover 8. A light source and a light sensor are comprised in the body 4. Reading of the image is effected by directing the beam from the light source onto the reflection original and having the reflected beam reach the light sensor.
On the other hand, it may be desired to read an image of, for example, a transparency film which is referred to as a "transparency original" hereinafter. In this case a sheet of white paper 12 is placed on the transparency original in order to reflect the beam from the light source by the sheet of white paper 12 whereby the image reader 2 can read the transparency original. The image reader 2 as shown in FIG. 1, however, can not read the image correctly because the cover 8 of image reader 2 can not adequately make the sheet of white paper 12 adhere to transparency original without any space between the two.
The detail of this condition is shown in FIG. 2A. A transparency original 10 to be read is placed face down on the transparency board 6 and the sheet of white paper 12 is placed on the top of the transparency original 10. Meanwhile in FIG. 2A, line images are described onto the transparency original 10. Portions 14 show line images in the transparency original 10. The beam .alpha. from the light source (not shown) passes through the transparency board 6 and portions of the transparency original 10 that show no image and it is reflected by the sheet of white paper 12 and reaches the light sensor (not shown).
Even if there is some space 16 between the transparency original 10 and the transparency board 6, the image reader 2 can read the image correctly without blurring if the space 16 is within the depth of field (see beam .beta.).
However, if there is space 18 between the transparency original 10 and the white paper 12 the image reader 2 can not read the image correctly even if the space 18 is within the depth of field, because, for example, as shown in FIG. 2B, the beam .gamma.1 from the light source passes through the transparency original 10, is reflected by the sheet of white paper 12 and is absorbed by the image portion 14 of the transparency original 10. That is, beam .gamma.1 from the light source which is supposed to reach the light sensor cannot reach the light sensor.
Meanwhile as shown in FIG. 3 there may also be some space 17 when reading a reflection original 11. The space 17 in FIG. 3 does not matter as long as it is within the depth of field.
In order to read the transparency original 10 correctly, it is necessary to prevent such space as space 18 shown in FIGS. 2A & 2B.
By the way, a frame for holding an original image for use in a camera for the purpose of preparation for printing is disclosed in the publication of the Japanese Utility model application SHO 51-19865. The detail of the frame for a camera is shown in FIG. 4. A transparency original 10 is set on a resilient board 20 made of sponge or the like. Then, the transparency original 10 is covered with a transparency board 6a. A packing 22 is installed in the outskirts of the resilient board 20 so that the transparency board 6a can adhere firmly to the resilient board 20. The detail of this condition is shown in section in FIG. 5. In this condition, when a vacuum pump (not shown) connected with a rubber hose is operated, it reduces the air pressure in the space formed by the transparency board 6a and the resilient board 20 and the packing 22, and the transparency board 6a is pressed against the resilient board 20. That is, the transparency original 10 is pressed against the transparency board 6a.
However the just described pre-existing methods for adjusting the bend of an image original contain problems that will be described in the following.
Firstly, such an apparatus as shown in FIG. 1 is easy to manipulate but cannot read the image correctly, as explained in FIGS. 2A & 2B.
Secondly, when such a frame for holding an original image in a camera for the purposes of preparation for printing as shown in FIG. 4 is applied to an image reader, the image reader can read the transparency original correctly but is more difficult to manipulate than such an image reader as shown in FIG. 1; even when reading the reflection original, the operation for reducing the air pressure must be effected.